This proposal is an experiment of nature that examines the profound effect of contrasting environment on neuroplasticity. Most current views of reading posit that the development, involvement and interaction of ortho-phonological and ortho-semantic systems depend on the statistical properties of languages. The overarching goal of this study is to take advantage of these differences, and perform a comprehensive neurocognitive investigation of how the complex process of learning to read in English (Eng.) is shaped online during the critical period of reading acquisition. This will be achieved by prolonged and intensive exposure to contrasting languages (Spanish, SP; Cantonese, Cn) that differentially stress these ortho-phonological and ortho-semantic systems. Sp has the same Roman alphabet as Eng., but with a different and more regular spelling-to-sound mapping that emphasizes phonological recoding. Cn uses the Chinese morphosyllabic writing system that is opaque and has weak character-to-sound mapping, presumably leading to greater reliance on ortho-semantic processes. Specifically, we will launch a prospective, longitudinal, and bidirectional examination of reading acquisition from kindergarten (K) to end of 2nd grade in 5 groups that is manipulated based on Eng. being their first or second language (L1 vs. L2) and the immersed language (Sp vs. Cn vs. none): native Eng. (L1) emerging readers in the U.S. starting Sp and Cn immersion programs initially learning primarily their L2 (L1Eng/L2Sp, L1Eng/L2Cn), L1 Sp and Cn speakers in the U.S. starting the same two-way immersion programs initially learning primarily their L1 (L1Sp/L2Eng, L1Cn/L2Eng), and Eng. monolinguals attending the same schools but not in the immersion programs (L1Eng). The main aims of the study are to investigate: 1) individual differences in the development of reading-related processes and brain circuitries in Eng., 2) how learning to read in Sp and Cn influence Eng. reading development given variant linguistic properties, 3) factors that affect interlinguistic/interliteracy influence (or transfer) , and 4) how these processes are shaped by early linguistic environment (e.g. early exposure to Eng., Cn versus Sp as their L1) and neurocognitive capacities (e.g. phonological awareness and related brain circuits, a significant risk factor of future reading impairment). The findings from this last exploratory aim will provide important initial insight into the influence of second language learning on children at-risk for developing reading disabilities, a population that is often discouraged from learning a foreign language. Children will be recruited from a local school district with which we have a collaborative relationship. The district is well-known for its extensive two-way immersion programs. This large-scale effort will advance theories of the neurocognitive processes underlying literacy development in Eng. by perturbing the system with languages of variant linguistic properties, advance understanding of the neurocognitive processes underlying multilingualism, and how minority students learn to read Eng. in the U.S.